This invention relates generally to a cutting tool for removing materials downhole from a well bore, such as pipe, casing, casing liners, tubing, jammed tools or the like, and more particularly, to such a cutting tool which is inserted within a well for removing predetermined members by first reducing the members to turnings or small chips for removal from the well.
Heretofore, various types of milling or cutting tools have been provided for cutting or milling existing pipe or casing previously installed in a well. Such tools normally have cutting blades on their lower ends and are lowered within the well or casing to be cut and then rotated in a cutting operation. A suitable drilling fluid is normally pumped down a central bore of the cutting tool for discharge beneath the cutting blades and an upward flow of the discharged fluid in the annulus outside the cutting tool removes the cuttings or chips resulting from the cutting operation from the well.
Milling tools for removing a section of existing casing or the like from a well bore have been provided heretofore. Sections of casings are removed for various purposes, such as, for example, to permit a side tracking operation in directional drilling, to provide a perforated production zone at a desired level, to provide cement bonding between a small diameter casing and the adjacent formation, or to remove a loose joint of surface pipe. Also, milling tools are used for milling or reaming collapsed casing, for removing burrs or other imperfections from windows in the casing system, for placing whipstocks in directional drilling, or for aiding in correcting dented or mashed-in areas of casing or the like.
A common milling tool has a plurality of blades spaced about the outer surface of the tool with the lower surfaces of the blades engaging the upper circular end surface of the pipe or casing in a cutting operation to chip or cut away progressively the end of the casing. Each blade takes a bite or cut from the upper end of the casing during rotation of the milling tool. The rate of penetration or cutting away of the casing is normally dependent on several factors, such as, for example, the rotational speed of the tool, the amount of weight on the tool, the number and type of blades, and the rate at which the chips or cuttings are removed from the well. Normal penetration rates heretofore have been around eight (8) to eleven (11) feet per hour and tools have required replacement after removal of around fifty feet or less of casing. Also, long turnings over six inches in length that tend to curl and internest with each other have been provided heretofore and in some instances the turnings have been several feet in length.
A critical factor in obtaining a high rate of penetration is in the removal of the metal scrap material and oftentimes the limiting factor to the cutting operation is the rate of removal of the metal scrap material. Long turnings or shavings tend to restrict, at times, such removal rates by internesting.